Low frequency oscillator



Feb. 13, 1940. J; MARKOWITZ 2,190,078

Low FREQUENCY oscILLAToR Filed Dec. 1, 1938 Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE gramm v y Low FREQUENCY osoILLA'roa Jerome Markowitz, Allentown, Pa. Application Decemberv 1, 1938, Serial No. 243,363

6 Claims.

This invention relates to oscillating space discharge devices and has particular reference to their use at low frequencies such as at audio frequency.

One object of the invention is to provide an improved oscillation generator of unusual frequency stability.

Another object of the invention is to provide an oscillation generator capable of furnishing a pure sine wave.

Another object of the invention is to provide an improved combination of oscillation generator and lag circuit keying system, said combination providing an output signal which builds up gradually and stops gradually.

Another object of the invention is to furnish an oscillation generator, the output of which builds up gradually and stops gradually on being keyed and without requiring the usual choke, condenser and resistor components ofthe ordinary lag circuit as known to the art.

Other objects and advantages of the invention will become apparent as the specification proceeds.

With the aforesaid objects in View, the invention consists in the novel combinations and ar rangements of parts hereinafter described in their preferred embodiments, pointed out in the subjoined claims, and illustrated in the annexed drawing, wherein like parts are designated by the same reference characters throughout the several figures.

In the drawing:

Fig. 1 shows a space discharge oscillator embodying the frequency stabilizing phase of thc invention.

Fig. 2 shows an oscillator embodying both the frequency stabilization and the lag circuit'.

Fig. 3 shows the invention as applied to a 40 Hartley type oscillator.

The advantages of the invention as here outlined are best realized when all of its features and instrumentalities are combined in oneand the same structure, but, useful devices may be produced embodying' less than the whole.

It will be obvious to those skilled in the art to which the invention appertains, that the same may be incorporated in severaldiiferent constructions. The accompanying drawing, therefore, is submitted merely as showing the preferred exemplincation of the invention.

This application is a continuation in part. of my application for radio tube oscillators filed October 27, 1937 now U. S. Letters Patent No. g5 2,140,267.

(CIL Z50- 36) Generally described the invention-provides a very stable oscillation generator of the space discharge type. The principles upon which this stabilization is based are similar to those contained lin the aforementioned patent, which in- 5 vention, however, specifically refers to oscillators of the Hartley class whereas the present invention deals with oscillators of the Colpitts group. These principles, however, may be applied to any oscillator, the frequency of which10 is controlled by a parallel connected inductance, capacity combination. As in my Letters Patent No. 2,140,267, the stability of the oscillator is improved to a marked degree byfselectingthat size of capacity in parallel with the inductance, which 1l is so large but desirably short of the size at which the oscillations of the space discharge device cease. In `order to provide a lag in the buildup and disappearance of the output of an oscillation generator of the type described it is only nece-t 20 sary to shunt a resistor across the keying means. The size of this resistor determines the amount of lag ofthe oscillator. The lowest resistance it is possible to use is that size unit whose resistance is so low but desirably greater than that resist- 25 ance at which the tube will oscillate. By using this size resistor the lag is very marked. increasing the resistance the lag effect becomes less noticeable until it practically disappears.

Obviously with this system key clicks may 136.30

eliminated entirely.

Another important point is that the lag increases as' the frequency decreases due to the loading effect of the L C constants of the oscillation circuit. The result is that ii these oscily lators. are used as the ultimate tone source for an electrical musical instrument such asan electricY organ the response or attack of the notes may very easily be made to simulate that of pipes or reeds. `Heretofore lag circuits consisted of o condenser, inductance combines which were relatively expensive. `To my knowledge this is the first time that the frequency control circuit of an oscillator is made to form part of the lag circuit. Moreover, the combination of this lag or 5 voltage buildup with an extremely stable oscillator is important because theoutput can be depended upon .tobeconstant in frequency during the period of varying voltage. In this connection it is Well'to remark that (assuming a fairly 50 low resistance oscillatorycircuit) the `cscillation frequency of this type oscillator is practically impervious to changes caused by supply voltage changes which assume even very extraordinary proportions. f

of the notes as upon the overtone content or phase*- relationship of the various harmonics of whicha given tone may be composed.

As was pointed out in the aforementioned patent the operation of an oscillator in vaccordance with the details of that invention enables `one to secure a sine wave with relative ease andminus the usual `by-pass condensers or filters. This' principle also holds true in the present invention.

The termaudio frequency as used in thisspecification refers to frequencies up to about 30,000v

cycles.

Referring in detail to the drawing Fig. 1 denotes an oscillator of the Colpittstype which embodies the invention. The same mayinclude a space discharge device I including a cathode, anode and grid. An inductance 2 may be con` nected between the grid I2v and the anode I3 through a source of direct current 3.v Two'condensers 4 and 5 are connected in series with each other but the series combine being connected parallel with the inductance 2 as shown. The `cathode II may be connected tothe junction of the condensers as indicated at IG and a chokev 6 is connected between the cathode and grid.v AnA output pick-up coil Ill may lead to any suitable load.

The total capacity of condensers series is made so large that it is just desirably short of the point at which the space 'discharge' device stops oscillating. The critical point' for stable operation may easily be determined in the following manner. The capacity /of the series combination, condensers 4 .and 5 are increased by steps. As this is done the outputfwill begin to gradually drop but when the maximum ca' pacity is approached it will be noticed that there is a sharp drop which is larger in proportion than the previous drops. This is the beginning ofthe region of stable operation although nearer the maximum capacity is approached the more stable is the operation. The aforementioned point of `critical capacity is usually within about to` 15' percent of the maximum capacity or that capacity at which the tube stops oscillating. However, no more exact data can be given as it depends upon various circuit constants such as typer of tube, operating voltage, or circuit resistance, etc. It suffices to say that with any given set of conditions the condenser capacity cited will result in unusual frequency stability. The ad` vantages of this invention are obtained at audio frequency.

In order to obtain a lag when controlling this oscillator, as by a contact 8, it is merely necessary to shunt the contact with a resistor 1 as shown in Fig. 2. As previously stated the lag .is con# trolled by the resistance-of the unit 1 and theL greatest lag is obtained when the resistance of I is so small but desirably greater than that resistance at which unit 1 will pass enough voltage to allow the tube to oscillate. Although in this drawing a Colpitts type oscillator isg shown,

4 and 5in it is to be understood that this principle applies to any oscillator the frequency of which is controlled by the combination of a condenser in parallel with an inductance. The capacitance of said condenser being so large but somewhat smaller than that capacity at which the space discharge device stops oscillating. In the drawing the circuit breaker is shown in the negative anode return circuit however it might be placed inthe-positiveranode branch of the circuit or even inserieswith the grid or cathode. The purpose of resistor 1 is to provide a means whereby the .oscillations will decay in a damped manner upon A the opening of said circuit breaker.

Fig. 3 illustrates this principle as applied to `an oscillator of the Hartley class. Here, the

inductance is connected between the anode I3 andthe grid I2 and an intermediate point of the inductanceis connected to the cathode II as indicated at I5. The condenser I4 is connected in parallel withftheinductance.` The capacity of condenser I4 is so large but desirably short of that capacity at which the space discharge de` vice I stops oscillating. The positioning of contact Sand resistor "I is self evident from the drawing; Contact 8 is a circuit breaker connected between the plate supply 3 and inductance 2 in Figure Zand Figure 3. The resistor 'I is connected across the contact 8.

Having thus described my invention what I claim is:

1. An oscillator of high degree of frequency stability comprising a space discharge device having a cathode, anode, and grid, an oscillatory frequency control circuit associated with said space discharge device, said circuit including an inductance connected between said anode and grid, a capacity means connected in parallel with at least a substantial portion of said inductance, the value ofsaidvcapacity means being so large that it is just short of vthat point which would prevent foscillation, means for connecting said cathode to said control circuit whereby feed-back is produced, a plate supply circuit for said oscillator, a circuitbreaker in said plate supply cir-- cuit, a resistor connected across said circuit breaker, the value of ythisresistance being so low that it is just greater than that resistance which will allow the tube to oscillate, whereby the oscillations will decay in a damped manner upon opening of said circuit breaker, said oscillator being constructed and arranged to operate at audio frequency. I

2. An oscillator in accordance with claim 1, wherein the means for connecting said cathode to said control circuit comprises a connection from Said cathode toan intermediate point on said inductance.

3. An oscillator in accordance with claim l, wherein said capacity means comprises two capacities in series and wherein the means for connecting said cathode to said control circuit cornprises a connection from said cathode to a point between said capacities in series.

4. An oscillator of high degree of frequency stability comprising a space discharge device having a cathode anode and grid, an oscillatory frequency control circuit` associated with said space discharge device, said circuit including an inductance connected between said anode and grid, a capacity means connected in parallel with at least asubstantal portion of said inductance, the value of said capacity means being so large that it is just short of -that point which would prevent oscillation, means for connecting .said

5. An oscillator in accordance with claim 4, wherein the means for connecting said cathode to said control circuit comprises a connection from said cathode to an intermediate point on said inductance,

6. An oscillator in accordance with claim 4, wherein said capacity means comprises two capacities in series and wherein the means for connecting said cathode to said control circuit comprises a connection from said cathode to a point 10 between said series capacities.

JEROME MARKOWITZ. 

